1. Field of the Invention
The present invention relates to an instrument to be used in artificial knee joint replacement surgery, and particularly to an instrument for finding a position of a predetermined portion in a patient.
2. Description of Related Art
When an artificial knee joint is attached to the knee joint of a patient, it is preferable to attach the artificial knee joint to the patient by using, as an index, an alignment in which the femoral head center, the knee joint center, and the second metatarsal bone of the patient are aligned in a straight line. However, since the femoral head center is located inside a human body, it is relatively difficult to confirm the position of the femoral head center, and thus surgery is sometimes performed in a state in which the position of the femoral head center is not accurately understood.
In this respect, Japanese Patent No. 4652481 discloses a femoral head center position identifying apparatus capable of identifying the position of the femoral head center, for example. This apparatus includes a marking plate that is to be arranged so as to cover a portion in which the femoral head center is located in a direction orthogonal to a frontal plane, a rotation arm having a rotation shaft that is to be arranged so as to extend in the direction orthogonal to the frontal plane, and a marker that is attached to the rotation arm and draws an arc on the marking plate with the rotation of the rotation arm. In this apparatus, the rotation arm is rotated at positions in a state in which a hip joint is positioned at a first position and a second position by being adducted and abducted, and thus the marker draws two arcs on the marking plate. The femoral head center can be identified as an intersection point of the two arcs drawn in such a manner.